1. Field of the Invention
The present invention relates to a reduced pressure processing system and a reduced pressure processing method used for processing a semiconductor substrate, a liquid crystal substrate, and the like and, more particularly, to a system having a load lock chamber used as a preliminary chamber for a process chamber.
2. Description of the Related Art
A reduced pressure processing system is used in various types of processes, e.g., ion implantation, dry etching, and film formation with respect to a substrate serving as a basic member of a semiconductor device or a liquid crystal panel. The reduced pressure processing system controls the internal atmosphere of a chamber to a desired reduced pressure and isolates a process atmosphere from the outer air atmosphere.
When vacuum processing such as ion implantation is to be performed with respect to a semiconductor wafer, if the atmosphere is mixed in a wide vacuum processing chamber, it takes much time to evacuate the chamber to a high vacuum again. For this reason, wafers are normally loaded/unloaded into/from the process chamber through a load lock chamber.
In this case, the load lock chamber is minimized in size to minimize the time required for evacuation. If moisture, process gas components, and the like adhere to the wall constituting the load lock chamber, the time required for evacuation is prolonged, resulting in a decrease in throughput.
FIGS. 1A to 1D show conventional reduced pressure processing systems as typical examples. FIG. 1A shows a system in which a process chamber PC is singly arranged. FIG. 1B shows a system in which load lock chambers LL1 and LL2 are arranged before and after a process chamber PC. FIG. 1C shows a system in which cassette chambers CC1 and CC2 are arranged before and after a process chamber PC. FIG. 1D shows a system in which load lock chambers LL1 and LL2 and cassette chambers CC1 and CC2 are respectively arranged before and after a process chamber PC.
Gate valves G, each having an automatic switching mechanism, are respectively attached to the entrance and exit to and from each chamber. Each gate valve G is controlled by a controller backed up by a computer system to be interlocked with a convey mechanism (not shown), an evacuation mechanism (not shown), and the like.
In each of the systems shown in FIGS. 1A to 1C, the internal pressure of each chamber must be restored to the atmospheric pressure (1 atm) every time a wafer is loaded/unloaded. Therefore, it takes much time to evacuate each chamber to a high vacuum again, resulting in a decrease in throughput.
Under the circumstances, as shown in FIGS. 1D and 2, a reduced pressure processing system is proposed, in which the load lock chambers LL1 and LL2 are respectively arranged between the process chamber PC and the cassette chambers CC1 and CC2 to reduce the influence of the atmosphere on the process chamber PC. In this case, the process chamber PC, the load lock chambers LL1 and LL2, and the cassette chambers CC1 and CC2 are respectively evacuated by evacuation systems 5. A wafer stage 2 on which a wafer W is placed is arranged in the process chamber PC located in the middle of the system. Wafer cassettes 4 are respectively stored in the cassette chambers CC1 and CC2. Each cassette 4 contains a plurality of semiconductor wafers W. Wafer convey mechanisms (convey robots) 3 are respectively arranged in the load lock chambers LL1 and LL2. Each convey mechanism 3 has an articulated arm and serves to convey the semiconductor wafer W from the cassette chamber CC1 to the process chamber PC or from the process chamber PC to the cassette chamber CC2, i.e., has a handling function.
In the system shown in FIG. 2, however, the outermost chamber (LL1, LL2, CC1 or CC2) must be restored to the atmospheric pressure at a predetermined frequency with the progress of processing in the process chamber PC. Therefore, it takes much time to evacuate the chamber to a high vacuum again, resulting in a decrease in throughput. Especially, if moisture contained in the outer air adheres to the chamber wall, heat of vaporization is generated in evacuation to transform the moisture into ice particles (a large number of micro ice) which are difficult to remove, thus prolonging the time required for evacuation and decreasing the throughput.
In order to prevent this, for example, an inert gas such as nitrogen is fed into a chamber before it is restored to the atmospheric pressure, and the gas is blown out during a loading/unloading operation with respect to a substrate to be processed. However, it is difficult to satisfactorily prevent the entrance of water molecules which fly in the atmosphere at a high molecular speed, and hence the above-described countermeasure is not effective.
In addition, if film formation processing such as CVD is performed in the process chamber, small quantities of source gases used for the processing, reaction gases produced therefrom, and the like remain in the process chamber. These residual gases flow into a preliminary chamber or a storage chamber and adhere to its inner wall and the like when a substrate to be processed or a processed substrate is loaded/unloaded. As a result, the interior of the chamber is contaminated, and a defective product may be produced.
Furthermore, various molecules such as water molecules adhere to the surface of a substrate to be processed while it is exposed to the atmosphere before a loading operation. Even if such a substrate is loaded into the chamber, and evacuation is started, since the molecules adsorbed in its surface cannot be removed quickly, it takes much time to attain a high vacuum, resulting in a decrease in throughput.